Biological Control

History

• Has a history of over 100 yrs.

• Track record of >5000 introduction against insect pests & >1000 against weeds

Concept and theories

• Natural control (NC)…has biocontrol component• Elements in Balance of nature• Population in equilibrium• Species diversity – in harmony within habitat.

• No one species continually increases OR decreases in relation to each other…

• Species niche concept… a given locality where a species is • more or less consistently abundant ; • others are less common ; • some species rarely encountered…

• cause varying niches !

Defination of BC

• centered on natural enemies (NE)• predators, parasitoids & pathogens ; • maintain density at a lower average.

• Present day workers… include• Host plant resistance • Autosterilisation• Modify environment • habitat manipulation• Genetic manipulation • GMOs and etc.

• Ecological basis… as opposed to technological.

Natural control

• A phase of natural control involving • importation• augmentation • conservation

• To regulate host population densities• To suppress pest number below economic injury• To modify environment favourable for Natural

Equilibrium• To modify environment, unsuitable for pest• To conduct mass release

• have insectary, intermittent inundative

• STRIVE to maintain for a long period…

– created at a stable environment (complex)

– achievable through population regulation

• equilibrium density (Smith, 1935)…

• steady state (Nicholson, 1933)…

• Discuss: GEP, ET, EIL, AT, Parasitoid/Predator introduction

• Stress levels in state of flux• the influence of rate of birth & death

• Have fluctuations• but consistent in population number year after year…

provided habitat not drastically disturbed.

• If population above GEP… natural regulating forces (biotic agents) will increase intensity (suppressive) with increase pest density… results in pest decline.

Food quality

Category of natural regulating forces

• Density-independent mechanism…

– Forces operating independent of density of organism.

• Density-dependent mechanism…

– Forces influenced by density of organism.

• What are Density Independent forces? -• Forces that determine ecological areas or boundaries

of the pest.• Mainly meteorological & physical

• rain, wind, temperature, • genetic defects,• accidents, natural catastrophe• agriculture activities… ploughing, • host plant destruction, phytosanitation, etc.

• What about in an agroecosystem ?• Man-made, temporary ecosystem,• Heaven for pest… monocroping…food a plenty• Biotic-natural forces… low activity• Pesticides disrupt biotic forces…• remedy!… conservation, augmentation!

• What are Density Dependent forces? -

• Forces that regulate the pest number present or surviving in that ecological area.

• Mainly predation, parasitism, diseases,

• inadequate food,

• limited nesting, limited hiding places & shelters,

• When overcrowded… leads to…

• cannibalism, suicidal dispersal,

• displaced to be exposed to…• hostile climate,

• vulnerable to predation & parasitism.

• What if permanent displacement of GEP caused by disturbances (natural or otherwise) ?

• 1. Major changes in the environment• Draining of swamp land… decreases the

number of mosquitoes.

• Dam the river… kills the fireflies in Kuala Selangor.

• Extensive cocoa cultivation… increase number CPB & mosquito bugs.

• Extensive development of cities without well planned drainage infrastructures… will increase cases of dengue!

• 2. Transferring pest insects from native home into a new habitat where the natural enemies are absent or ineffective…

• a case of introduced (exotic) pest, like DBM !

• Oil palms in the early years were poor yielding, why? This is a case of transferring of plant into Malaysia without its natural pollinators ! … small Fruit Bunch.

• Present approach to population management

• Integrate Natural Enemies with other control measures… IPM

• Still not a guaranteed success… why ?• The key question is…

• can the Natural Enemies regulate pest population substantially, continuously for long periods (yrs)… not just immediate mortality in one yr., esp. in the case of predators, parasitoids & disease agents

• So IPM must be pest oriented…in monocrop.

• What about ICM ?… crop diversity helps.